Ok, I've made it clear that I'm not about to theorycraft, but I'd like to take an over-simplified look at the raid buffs and debuffs that all the classes can bring to the party. Over at MMO-Champion there's a nice summary of the potential buffs and debuffs (by buff/debuff) that will be in the upcoming Cataclysm expansion.
Taking the elementary approach, that is counting and adding, I'd like to show you what each class has to benefit the raid/group:
Let's assume that a debuff on the bad guy is considered a buff to the group, or at least part of it, let's take a glance at who, by the numbers, brings the most utility to the raid group.
Shaman (accross all talent specs)
Interestingly, the Shaman will provide no debuff on any of the targets, the only thing a Shaman can do is enhance those around him/her.
The median total is 9 (Warlock, Warrior, Paladin), the mean is 7.6 buffs. In last place is the Priest...no surprise there, a class with two healing trees buffs people by giving them life. The Shadow Priest giving out, aside from Fortitude, only two other buffs. Sad, just sad. Maybe they will make up for it by filling the top spot as the best non-pure-dps DPS spec in the game. Then again, probably not. So sad.
On the bright side, aside from the lowly Priests & Hunters, everyone else brings 7-9 buffs/debuffs to the raid. I guess it would have been too obvious that the homoginization plans devised by Blizzard in their secret underground caverns are real if all had been given either the same buff or 8 each. Even though there is not one buff that only one class can bring (like Hero/Bloodlust is now), there's still a nice mix and every spec of every class gets to contribute something.
I'll leave it to the nerds to tell you what the optimal mix of class/spec will be for the Cataclysm 10 man raids. I don't really care what it is, all I know is that whatever group you get together, as long as it's not all Paladins, you'll be able to get many of the raid buffs listed, and I don't think that's necessarily a bad thing. Need replenishment? Great, that guy who insists on raiding as Frost Mage can give you that. I look at it as I will be able to give something to the raid group no matter my chosen class/spec combo. Clearly Shaman and Paladins will be the biggest buffers in Cataclysm, but that really isn't much of a change.